Dielectric interface films and methods therefor

ABSTRACT

An ultrathin aluminum oxide and lanthanide layers, particularly formed by an atomic layer deposition (ALD) type process, serve as interface layers between two or more materials. The interface layers can prevent oxidation of a substrate and can prevent diffusion of molecules between the materials. In the illustrated embodiments, a high-k dielectric material is sandwiched between two layers of aluminum oxide or lanthanide oxide in the formation of a transistor gate dielectric or a memory cell dielectric. Aluminum oxides can serve as a nucleation layer with less than a full monolayer of aluminum oxide. One monolayer or greater can also serve as a diffusion barrier, protecting the substrate from oxidation and the high-k dielectric from impurity diffusion. Nanolaminates can be formed with multiple alternating interface layers and high-k layers, where intermediate interface layers can break up the crystal structure of the high-k materials and lower leakage levels.

REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the priority benefit under 35U.S.C. § 119(e) to prior provisional application No. 60/239,040, filedOct. 10, 2000, entitled METHOD OF DEPOSITING OXIDE THIN FILMS,provisional application No. 60/244,789, filed Oct. 31, entitled ALUMINUMOXIDE INTERFACE FILMS AND METHODS THEREFOR, and provisional applicationNo. 60/247,115, filed Nov. 10, 2001, entitled DIELECTRIC INTERFACE FILMSAND METHODS THEREFOR.

FIELD OF THE INVENTION

[0002] The present invention relates generally to thin dielectric filmsin integrated circuits, and more particularly to interface layers fordielectric thin films.

BACKGROUND AND SUMMARY OF THE INVENTION

[0003] Atomic Layer Deposition (ALD) is a self-limiting process, wherebyalternated pulses of reaction precursors saturate a substrate and leaveno more than one monolayer of material per pulse. The precursors anddeposition conditions are selected to ensure self-saturating reactions.For example, an adsorbed layer in one pulse leaves a surface terminationthat is non-reactive with the gas phase reactants of the same pulse. Asubsequent pulse of different reactants do react with the previoustermination to enable continued deposition. Thus, each cycle ofalternated pulses leaves no more than about one molecular layer of thedesired material. The principles of ALD type processes have beenpresented by T. Suntola, e.g. in the Handbook of Crystal Growth 3, ThinFilms and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14,Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B.V. 1994.

[0004] Recently, these processes have been suggested for use insemiconductor fabrication. However, due to the slowness of the process(depositing one atomic layer of material per cycle), ALD has been oflittle practical benefit for current commercial process flows.

[0005] One material for which ALD processes have been developed isaluminum oxide (Al₂O₃). The deposition of aluminum oxide by ALD typeprocesses is well known in the art. See, e.g., E.-L. Lakomaa, A. Root,T. Suntola, “Surface reactions in Al₂O₃ growth from trimethylaluminiumand water by atomic layer epitaxy”, Appl. Surf. Sci. 107 (1996) 107-115.This article is incorporated herein by reference.

[0006] In accordance with one aspect of the invention, an oxideinterface layer is provided for a dielectric structure positionedbetween two conductive materials in an integrated circuit. The preferredembodiments employ metal oxide thin films for the interface layer,particularly aluminum oxide and lanthanide (“rare earth”) oxides, whichcan advantageously remain amorphous even after exposure to hightemperatures. The oxide interface layer is preferably deposited by anatomic layer deposition (ALD) type process. Advantageously, thepreferred interface materials do not readily react with many othermaterials and are very good barriers against the diffusion of molecules,atoms and ions. Al₂O₃ and lanthanide oxides can be deposited by ALDprocesses with excellent control; extremely thin, uniformly thick layerscan be formed without pinholes and at a wide range of substratetemperatures, depending on the source chemicals. Thus, ALD enables oxidelayers thin enough to serve as an interface layer without adverselyaffecting electrical properties of the integrated circuit.

[0007] In accordance with another aspect of the invention, a highdielectric constant (high-k) dielectric structure is provided in anintegrated circuit. The high-k dielectric structure comprises a firstinterfacial layer of aluminum oxide, a layer of high-k material directlyadjacent the first interfacial layer, and a second interfacial layer ofaluminum oxide directly adjacent the high-k material. The high-kmaterial preferably has a dielectric constant of at least about 5, andmore preferably at least about 10. Exemplary high-k materials include,but are not limited to, zirconium oxide (ZrO₂), hafnium oxide (HfO₂),titanium oxide (TiO₂), tantalum oxide (Ta₂O₅), barium strontium titanate(BST), strontium titanate (ST), barium titanate (BT), lead zirconiumtitanate (PZT), lead strontium titanate (PST), strontium bismuthtantalate (SBT), metal silicates, aluminum nitride and nitrided metaloxides (e.g., Ta_(x)O_(y)Nb_(z), Nb_(x)O_(y)N_(z)). The aluminum oxideinterfacial layers can also be replaced by lanthanide oxide layers.

[0008] The dielectric structure is positioned between a first conductorand a second conductor. Aluminum oxide and lanthanide oxides have beenfound particularly beneficial as interface layers between dopedsemiconductor structures, such as a doped silicon substrate in atransistor structure, and other dielectric materials. Furthermore, theirexcellent interfacial properties facilitate advanced materials. Forexample, aluminum oxide has been found particularly advantageous betweenhigh-k materials and poly-SiGe gate electrodes. During CVD of SiGe,nucleation over ALD Al₂O₃ during initial phases of deposition was foundsuperior to that over SiO₂, thus speeding overall deposition rates.Other gate electrode materials may also be made possible due to superiornucleation of depositions thereover and protection against corrosion andimpurity diffusion offered by the aluminum oxide interface between thegate electrode and the high-k material. In another example, a high-kdielectric structure (including a high-k material sandwiched betweenaluminum or lanthanide oxide interfacial layers) serves as a capacitordielectric in an integrated circuit. The interfacial layers are ofparticular utility over silicon electrodes, such as hemisphericalgrained silicon (HSG-Si), but are also useful barriers for protection ofother oxidation-susceptible electrode materials.

[0009] Another aspect of the present invention is an aluminum oxidelayer or a lanthanide oxide layer located between two materials, wherethe oxide layer has a thickness between one full molecular monolayer andabout 4 molecular monolayers. The oxide layer prevents diffusion ofmolecules from one material to the other.

[0010] Another aspect of the invention provides a method of preventingthe oxidation of a substrate by depositing a layer of aluminum oxide orlanthanide oxide on the substrate by an ALD type process. Substratesotherwise susceptible to oxidation include conventional semiconductorsubstrates, such as single-crystal silicon wafers or epitaxial layers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] These and other aspects of the invention will be readilyunderstood in view of the description below and the appended drawings,which are meant to illustrate and not to limit the invention, and inwhich:

[0012]FIG. 1 is a schematic view of an integrated circuit transistor,including aluminum oxide or lanthanide oxide interfacial layers, inaccordance with the preferred embodiments.

[0013]FIG. 2 is a flow chart of a preferred method of depositingaluminum oxide using an ALD process.

[0014]FIG. 3 is a flow chart illustrating a process of forming gatestacks, in accordance with a preferred embodiment of the invention.

[0015]FIG. 4 is a schematic view of an integrated circuit capacitorcomprising a nanolaminate structure, in accordance with the preferredembodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] While illustrated in the context of transistor gate stacks, theskilled artisan will readily find application for the principles andadvantages disclosed herein to other situations where similar electricaland physical properties at an interface are desired.

[0017] The present invention utilizes a thin dielectric film as aninterface layer between two materials to prevent a detrimental reactionbetween them. A detrimental reaction may include a chemical reaction ordiffusion. For example, Al₂O₃ can be placed as a lower interface layerunder any high-k material, or as a top interface layer that iscompatible with polysilicon or SiGe (alloy of silicon and germanium).The primary example herein of such a dielectric interface film is Al₂O₃;however, as discussed below, lanthanide oxides have also been found tohave excellent interfacial properties in a dielectric stack.

[0018] Al₂O₃ or lanthanide oxide thin films may be used to prevent asolid phase from reacting with the surroundings. For example, the solidphase can be deposited directly over an Al₂O₃ thin film. Alternativelyan Al₂O₃ or lanthanide oxide layer can be deposited directly over thesolid phase. In a third variation, the solid phase can be sandwichedbetween two Al₂O₃ or lanthanide oxide thin films.

[0019] More particularly, Al₂O₃ can act as a diffusion barrier interfaceand prevent the diffusion of molecules, atoms or ions from a solid phaseon one side of the Al₂O₃ layer to a solid phase on the other side of theAl₂O₃ layer. For example, Al₂O₃ may serve as a boron diffusion barrier.For a diffusion barrier function of an interface layer, at least onemolecular monolayer of Al₂O₃ is desired, preferably between about 1 and4 monolayers, and more preferably between about 1 and 2 monolayers. Interms of absolute thickness, the aluminum oxide interfacial layerpreferably has a thickness between about 3 Å and 15 Å, more preferablybetween about 3 Å and 9 Å.

[0020] An Al₂O₃ surface can also act as a nucleation layer at a topinterface for further solid phase growth. In the context of integratedcircuit formation, a high dielectric material can be deposited on alower aluminum oxide interface layer. An in situ doped silicon layer(such as boron-, arsenic- phosphorus- or germanium-doped silicon) canalso be directly deposited directly over a top aluminum oxide interfacelayer on an Al₂O₃ thin film in the production of a gate dielectric. Thenucleation layer speeds initial deposition of silicon-containing layers,particularly in situ doped silicon, which can have long nucleation timesover SiO₂, as is known in the art. Accordingly, throughput can beradically improved. To serve as a nucleation layer, as little as onecycle of an ALD Al₂O₃ process (representing less than one monolayer,typically about ⅓ of a monolayer) can improve nucleation times ofdeposition thereover, especially for the top aluminum oxide interfacelayer between a high-k material and a gate electrode. Such a partialmonolayer will typically manifest as aluminum oxide “dots” evenly spreadover the substrate. These separated dots are sufficient to provide rapidand uniform nucleation across the substrate. However, it is preferredfor most integrated circuit contexts to produce an aluminum oxide layerthick enough to also serve as a barrier layer, as discussed in theprevious paragraph.

[0021] The invention is particularly useful, therefore, in forming upperand/or lower interfaces on a high-k dielectric constant material, suchas ZrO₂. For example, an Al₂O₃/ZrO₂/Al₂O₃ sandwich structure hasexcellent physical and electrical properties in a gate dielectric. Lowerequivalent oxide thickness (EOT) is obtained when Al₂O₃ is used insteadof SiO₂ as an interface layer, since the dielectric constant of Al₂O₃(on the order of 10) is higher than that of SiO₂. Other high-k materialsinclude hafnium oxide (HfO₂), titanium dioxide (TiO₂), tantalum oxide(Ta₂O₅), barium strontium titanate (BST), strontium titanate (ST),barium titanate (BT), lead zirconium titanate (PZT) and strontiumbismuth tantalate (SBT). These materials and other, similar materials,while advantageously demonstrating high dielectric constants, tend to beunstable and/or inconsistent in composition, and also tend to requirehighly oxidizing environments during deposition. Thus, to preventoxidation of the underlying substrate, a lower aluminum oxide interfacelayer is preferably in the range of about 1-4 monolayers in thickness(representing about 3-15 ALD cycles with TMA and water), more preferablybetween about 1 monolayer and 2 monolayers. In addition to minimizingimpurity and oxygen diffusion, an Al₂O₃ layer can prevent theagglomeration of a high-k material during the high-k deposition.

[0022] The skilled artisan will appreciate that similar aluminum oxidesandwiches will have application to memory cell capacitors.

[0023] For the purpose of the present invention, an “ALD type process”designates a process in which deposition of vaporized material onto asurface is based on sequential and alternating self-saturating surfacereactions. The principles of ALD type processes have been presented byT. Suntola, e.g. in the Handbook of Crystal Growth 3, Thin Films andEpitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14, AtomicLayer Epitaxy, pp. 601-663, Elsevier Science B.V. 1994, the disclosureof which is incorporated herein by reference.

[0024] “Reaction space” designates a reactor or reaction chamber inwhich the conditions can be adjusted so that deposition by ALD ispossible.

[0025] The present invention provides an oxide interface between two ormore materials. Preferably, one of the materials is a high dielectricmaterial, such as ZrO₂. The high dielectric material preferably has adielectric constant greater than 5. More preferably the high dielectricmaterial has a dielectric constant greater than about 10. Such “high-k”materials include oxides of Group 4 and Group 5 metals (e.g., Ti, Zr,Hf, V, Nb, Ta), as well as more complex oxides. As noted below, “high-k”materials can also include lanthanide oxides, such as lanthanum oxide(k≈21), neodymium oxide (k≈16) and cerium dioxide (k≈15).

[0026] In one aspect, the present invention provides an aluminum oxidesandwich, wherein two aluminum oxide layers are used as interface layersseparating three other materials. The structure of such an aluminumoxide sandwich can be represented by material 1/Al₂O₃/material2/Al₂O₃/material 3. Preferably, materials 1 and 3 are conductors in anintegrated circuit, while material 2 is a thin dielectric film. “Thin,”in this context, refers to a dielectric layer thin enough to serve as acapacitor dielectric (in combination with the Al₂O₃ interface layers)when charge is stored on one of the conductive materials 1 and 3. Suchcapacitor dielectric functions are most typically found in gatedielectrics and memory cell dielectrics.

[0027] In the embodiment of FIG. 1, an aluminum oxide or lanthanideoxide sandwich 15 is part of a transistor gate electrode. FIG. 1 depictsa cross section of such an arrangement. Aluminum oxide or lanthanideoxide layers 10, 12 directly contact either side of a dielectricmaterial layer 20. The oxide layers 10, 12 serve as interfacial layersbetween the dielectric material 20 and the overlying gate electrode 30,and between the dielectric material and the underlying silicon substrate40. Preferably, the gate electrode comprises polycrystalline silicon,and more preferably poly-SiGe. In the oxide sandwich 15, the middledielectric layer is preferably characterized by a high dielectricconstant (high-k), comprising ZrO₂ in the illustrated embodiment. Inother arrangements, it will be understood that the high-k material cancomprise multiple materials, either as a ternary structure or a laminate(see FIG. 4) of multiple high-k material layers. As noted above, wherethe oxide layers 10, 12 comprise aluminum oxide, they preferably eachhave a thickness between about 1 Å (⅓ monolayer) and 15 Å (4monolayers), more preferably between about 3 Å and 9 Å, and mostpreferably between about 3 Å and 6 Å.

[0028]FIG. 3 illustrates an exemplary sequence for forming interfaciallayers in accordance with the preferred embodiments. The sequence shownis for forming a transistor gate dielectric structure between asemiconductor substrate and a gate electrode, including aluminum oxideinterface layers sandwiching a high-k material. Initially, thesemiconductor substrate surface can be optionally prepared 70 forsubsequent deposition by ALD. Such preparation can include, for example,water or alcohol treatment, as described in more detail below.Subsequently, a first aluminum oxide interface layer is deposited 72 byALD. A high-k layer is deposited 74 thereover. This layer can also bedeposited in situ within the same reaction chamber. A second aluminumoxide interface layer is then deposited 76 by ALD over the high-k layer.A transistor gate electrode is then deposited 78 over the secondinterface layer. A cluster tool having in situ wafer cleaning, ALD andCVD modules can be employed, particularly where the interface layer isformed by ALD and the high-k material is formed by CVD or other method.

THE OXIDE INTERFACE FORMATION PROCESS

[0029] According to one preferred embodiment, alternating vapor-phasepulses of an aluminum or lanthanide source chemical and an oxygen sourcechemical are fed to a reaction chamber having a reduced pressure andcontacted with a heated substrate surface to form an aluminum orlanthanide oxide thin film. The source chemical pulses are separatedfrom each other by removal steps, preferably with flowing inert or noblegas, so that gas phase reactions are avoided and only self-saturatingsurface reactions are enabled. The general process will be betterunderstood by reference to FIG. 2, exemplifying aluminum oxidedeposition by ALD, discussed below.

THE SOURCE MATERIALS 1. Metal Source Materials

[0030] The aluminum or lanthanide source chemical is selected from agroup of aluminum and lanthanide compounds that are volatile andthermally stable at the substrate temperature.

1.1 Alkyl Aluminum Compounds

[0031] Alkyl aluminum compounds have at least one aluminum-carbon bond.Examples of source compounds are trimethylaluminum (CH₃)₃Al,triethylaluminum (CH₃CH₂)₃Al, tri-n-butylaluminum (n-C₄H₉)₃Al,diisobutylaluminum hydride (i-C₄H₉)₂AlH, diethylaluminum ethoxide(C₂H₅)₂AlOC₂H₅, ethylaluminum dichloride (C₂H₅)₂AlCl₂, ethylaluminumsesquichloride (C₂H₅)₃Al₂Cl₃, diisobutylaluminum chloride (i-C₄H₉)₂AlCland diethylaluminum iodide (C₂H₅)₂AlI. These compounds are commerciallyavailable from, e.g., Albemarle Corporation, USA.

[0032] In the preferred embodiment, trimethylaluminum (CH₃)₃Al is usedas the aluminum source chemical.

1.2 Aluminum Alkoxides (Al—O—C Bond)

[0033] Aluminum alkoxides contain an aluminum-oxygen-carbon (Al—O—C)bond. Examples of source compounds are aluminum ethoxide Al(OC₂H₅)₃,aluminum isopropoxide Al[OCH(CH₃)₂]₃ and aluminum s-butoxide Al(OC₄H₉)₃.These compounds are commercially available from, e.g., Strem Chemicals,Inc., USA.

1.3 Aluminum Beta-diketonates

[0034] Aluminum beta-diketonates have organic ligands coordinated toaluminum via oxygen atoms. Examples of source compounds are aluminumacetylacetonate Al(CH₃COCHCOCH₃)₃, often shortened as Al(acac)₃, andtris-(2,2,6,6-tetramethyl-3,5-heptanedionato)aluminum, usually shortenedas Al(thd)₃, Al(TMHD)₃ or Al(DPM)₃. Volatile halogenated aluminumbeta-diketonates are also commercially available, such as aluminumhexafluoroacetylacetonate Al(CF₃COCHCOCF₃)₃, often shortened asAl(hfac)₃. These compounds are commercially available from, e.g., StremChemicals, Inc., USA.

1.4 Aluminum Halides

[0035] Volatile, purely inorganic aluminum halides such as aluminumchloride AlCl₃ or Al₂Cl₆, aluminum bromide AlBr₃, and aluminum iodideAlI₃ may be used as precursors

1.5 Anhydrous Aluminum Nitrate

[0036] At low substrate temperatures, anhydrous aluminum nitrate can beused as an aluminum source chemical for ALD. The synthesis of anhydrousAl(NO₃)₃has been described by G. N. Shirokova, S. Ya. Zhuk and V. Ya.Rosolovskii in Russian Journal of Inorganic Chemistry, vol. 21, 1976,pp. 799-802, the disclosure of which is incorporated herein byreference. The aluminum nitrate molecule breaks into aluminum oxide whenit is contacted with organic compounds, such as ethers.

1.5 Anhydrous Aluminum Nitrate

[0037] Lanthanides can be made volatile with selected ligands thatprevent interaction between lanthanide atoms in the precursor or source.Examples of suitable ligands include beta-diketonates, such as thd(thd=2,2,6,6-tetramethyl-3,5-heptanedione) and alkyldisilazanes, such ashmds (hmds=N(Si(CH₃)₃)₂). Physically stable lanthanides from which toform these precursors include scandium (Sc), yttrium (Y), lanthanum(La), cerium Ce, praseodymium (Pr), neodymium (Nd), samarium (Sm),europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium(Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

2. Oxygen Source Materials

[0038] Volatile or gaseous compounds that contain oxygen and are capableof reacting with an aluminum source compound on the substrate surfaceresulting in the deposition of aluminum oxide are used as oxygen sourcematerials. The choice of oxygen source material may be influenced by thesubstrate on which the aluminum oxide layer is to be deposited and thuswhether the aluminum oxide thin film will form a top interface layer ora bottom interface layer.

[0039] In the production of an aluminum oxide sandwich on a siliconsubstrate, hydrogen peroxide, ozone and oxygen with unpaired electronsare preferably used only for the top interface. Water and alcohols, suchas methanol, ethanol and isopropanol, may be used for any interface, asthey are less liable to oxidize the underlying silicon during thedeposition process. Alcohols are especially reactive with aluminumhalides.

THE CHEMISTRY ALD of Aluminum Oxide

[0040] A substrate is loaded into a reaction space. The reaction spaceis adjusted to the desired temperature and the gas atmosphere of thereaction space is adjusted to the desired pressure. A repeatable processsequence including four basic steps, as depicted in FIG. 2, is begun.Aluminum oxide deposition is shown, though the skilled artisan willappreciate, in view of the present disclosure, that a similar processcan be used to deposit lanthanide oxides.

[0041] With reference to FIG. 2, a vapor phase pulse 50 of an aluminumsource chemical is introduced into the reaction space and contacted withthe substrate surface. After a first contact time the surplus aluminumsource chemical and any possible reaction byproducts are removed 55 fromthe reaction space by varying the reaction space pressure and/or byinert gas flow. After a first purging time a vapor phase pulse 60 of anoxygen source is introduced into the reaction chamber and contacted withthe substrate surface. After a second contact time the surplus oxygensource chemical and any possible reaction byproducts are removed 65 fromthe reaction space by varying the reaction space pressure and/or byinert gas flow. After a second purging time the illustrated processcycle is repeated until an aluminum oxide thin film of a desiredthickness is obtained. Finally, the substrate having the thin film isunloaded from the reaction chamber or another thin film process isstarted.

[0042] It will be appreciated that a similar sequence to that of FIG. 2,with the aluminum source chemical replace by a lanthanide sourcechemical pulse, will result in deposition of a lanthanide oxide layer.

SURFACE PREPARATION PRIOR TO ALD

[0043] As illustrated in FIG. 3, substrate surfaces may benefit from asurface pretreatment 70 prior to ALD thereover. A few exemplary surfacepreparation treatments are provided below, depending upon the startingsurface.

Silicon Substrate with Surface Native Oxide

[0044] Substrates with native oxide will typically not require surfacepreparation. Rather, the above-described ALD process (e.g., with theTMA/purge/water/purge cycle of Example 1 below) will initially reactwith the native oxide and deposition will proceed as discussed above.

Silicon Substrate with an Etched Silicon Surface

[0045] It is unlikely that aluminum alkyls, such as (CH₃)₃Al, can attachon a hydrogen-terminated silicon surface. However, a first water pulsemay react with the silicon surface and leave a hydroxyl terminated (—OH)or oxygen bridged (Si—O—Si) silicon surface that serves as a startingsurface for the chemisorption of aluminum alkyls. The process describedabove and illustrated in FIG. 2 can proceed thereafter, as the preferredprecursors readily react with Si0 ₂ to deposit Al₂O₃ thereover.

Ozone Treatment of Silicon Surface

[0046] Ozone reacts with silicon and thus forms a silicon dioxide layeror increases the thickness of the native silicon dioxide layer,depending of course upon temperature, exposure duration and O₃concentration. Either a native oxide or H-terminated silicon surface canbe thus prepared for the formation of an aluminum oxide thin film withan initial ozone pulse.

REPLACEMENT REACTION

[0047] According to one embodiment, a silicon dioxide surface(preferably a very thin native oxide) can be treated with an aluminumsource chemical to produce an exchange reaction with the surface,replacing SiO₂ with Al₂O₃. For example:

1.5SiO₂(s)+2AlL₃(g)→Al₂O₃(s)+1.5SiL₄(g) ΔG _(f)(temp./° C.)=<0 kJ   [1]

[0048] L is a ligand, preferably a halide such as chloride, bromide oriodide, more preferably comprising chloride, as set forth in Example 3below.

[0049] The Gibb's free energies can be calculated, e.g., with HSCChemistry, Ver. 4.1, Outokumpu Research Oy, Pori, Finland.

[0050] The exchange reaction is preferably applied to relatively thinlayers. The aluminum oxide layer formed by the exchange reaction is usedas an interface layer between silicon and a high-k material

LANTHANIDE OXIDES

[0051] Amorphous aluminum and lanthanide oxides deposited by ALD areutilized in dielectric thin films. These oxides are combined with high-kmaterials to produce state-of-the-art gate dielectrics and integratedcircuit capacitor dielectrics, particularly for integrated memory cells.Exemplary transistors include silicon or SiGe gate electrodes, andmonocrystalline silicon or GaAs substrates. Exemplary memory devicesinclude dynamic random access memory (DRAM), synchronous DRAM (SDRAM),direct Rambus™ DRAM (DRDRAM), static random access memory (SRAM), andnon-volatile memory devices. Non-volatile memory devices include readonly memory (ROM), programmable ROM (PROM), erasable programmable ROM(EPROM), electrically erasable programmable ROM (EEPROM) and flashmemory devices.

[0052] The lanthanide elements, such as lanthanum (La), yttrium (Y) andscandium (Sc), have also been known as rare earth elements. The use ofthe word “rare” in this term is misleading because these elements arenot particularly rare on Earth. As stated by N. N. Greenwood and A.Earnshaw in CHEMISTRY OF THE ELEMENTS, Pergamon Press Ltd. 1986, cerium(Ce) is 5 times as abundant as lead (Pb). Even thulium (Tm), the rarestof the stable rare earth elements, is more abundant than iodium (I).Lanthanides are usually extracted either from monazite or bastnaesiteminerals. It can be seen that, from an economical point of view, theutilization of rare earths for thin film structures is quite feasible.As used herein, “physically stable lanthanides” are defined as scandium(Sc), yttrium (Y), lanthanum (La), cerium Ce, praseodymium (Pr),neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb) and lutetium (Lu).

[0053] Lanthanide compounds are similar to compounds of aluminum incertain aspects. Aluminum oxide Al₂O₃ has a very high melting point(2070° C.), while the melting point of yttrium oxide Y₂O₃ is 2410° C.and that of lanthanum oxide La₂O₃ 2307° C. All of these oxides are alsoquite inert and have high resistivities. Bonds between the metal andoxygen atoms are very strong. For example, Al—O has a bond strength of512 kJ/mol, La—O has a bond strength of 799 kJ/mol and Y—O has a bondstrength of 715 kJ/mol. CRC HANDBOOK OF CHEMISTRY AND PHYSICS, CRCPress, Inc. High melting points and bond strengths indicate thatamorphous aluminum and lanthanide oxides can be heated to hightemperatures without crystallization. Chemical inertness is beneficialfor keeping nanolaminate layers (as described below) separated from eachother and from surrounding materials and having a stable dielectricstructure during the fabrication and lifetime of the manufactureddevices.

NANOLAMINATE DIELECTRICS

[0054] Nanolaminate dielectric structures have been reported in thepast. For example, Ritala et al. have made Al₂O₃—TiO₂ nanolaminates byALD using TiCl₄, AlCl₃, H₂O as source chemicals, where the TiO₂ layerswere polycrystalline and the Al₂O₃ layers were amorphous. M. Ritala, M.Leskela, L. Niinisto, T. Prohaska, G. Friedbacher and M. Grassenbauer,“Surface roughness reduction in atomic layer epitaxy growth of titaniumdioxide thin films,” Thin Solid Films, Vol. 249 (1994), pp. 155-162.Al₂O₃ layers placed in the film reduced the surface roughness of theTiO₂ thin film. The article conducted depositions at 500° C. andconcludes that alternating 925 cycles of TiO₂ deposition with 75 cyclesof Al₂O₃ deposition minimized surface roughness, as measured bymaximized optical transmission. Ta₂O₅—Al₂O₃ nanolaminates are alsodisclosed in H. Kattelus, M. Ylilammi, J. Saarilahti, J. Antson and S.Lindfors, “Layered Tantalum-Aluminum Oxide Films Deposited by AtomicLayer Epitaxy,” Thin Solid Fihns, Vol. 225 (1993), pp. 296-298. TaCl₅,AlCl₃ and H₂O were used as source chemicals. With depositions conductedat 300° C. and no post-deposition treatment, the authors conclude thateven small amounts of aluminum oxide introduced as thin layers in thetantalum oxide results in improvement in the dielectric properties.

[0055] According to one embodiment of the present invention, ananolaminate consists of alternating crystalline and amorphous layers ofmetal oxides. Amorphous layers decrease the leakage current through thenanolaminate while crystalline layers can increase the dielectricconstant of the whole nanolaminate structure. According to anotherembodiment of the present invention, the nanolaminate contains onlyamorphous metal oxide layers for obtaining extremely low leakage currentwhile having sufficiently high dielectric constant.

[0056] “High-k” material, for the purposes of describing layers in thenanolaminate structure of the present embodiment, is defined as a metaloxide that has higher dielectric constant than Al₂O₃ (about 10). High-kmetal oxides that can be utilized in the metal oxide nanolaminateinclude oxides of elements in Group 4, (Ti, Zr and Hf) and Group 5 (V,Nb and Ta) of the periodic table of elements. “High-k” materials canalso include lanthanide oxides, such as lanthanum oxide (k≈21, neodymiumoxide (k≈16) and cerium dioxide (k≈15).

[0057] Advantageously, employing amorphous layers, such as Al₂O₃ andlanthanide oxides, in the nanolaminate structure makes it possible toutilize other high-k metal oxides that may have rather high leakagecurrent themselves. Such “leaky” materials can include binary compounds,(e.g., SnO₂, WO₃), ternary compounds (e.g., metal titanates such as Ba,Sr, Ca, Mg or Pb titanates; metal zirconates such as PbZrO₃; and metalniobates such as Pb₅Nb₄O₁₅) and quaternary compounds (e.g.,Ba—Zn—Ta—oxide and Zr—Sn—Ti oxide). As these complex oxides can havemuch high dielectric constant values, reaching into the 100's, it wouldbe advantageous if they could be incorporated into dielectric stackswithout degrading yield or performance.

[0058] According to one embodiment of the present invention, the crystalgrowth of a high-k metal oxide can be interrupted with an intermediateamorphous metal oxide layer, particularly Al₂O₃ or a lanthanide oxide,in a stack of dielectric layers (a dielectric “nanolaminate”). Theseintermediate amorphous layers affect the crystallization temperature ofthe dielectric material. Decreasing the individual metal oxide layerthickness in the nanolaminate structure, while keeping the totalthickness of the nanolaminate unchanged, increases the crystallizationtemperature of the high-k metal oxide. Increased crystallizationtemperature can effectively decrease the leakage current through thedielectric material, since an amorphous thin film will demonstrate alower leakage current than a corresponding crystalline thin film.

[0059] From this standpoint, the most basic nanolaminate constructioncomprises at least two high-k layers separated by a thin aluminum oxideor lanthanide oxide film, thereby interrupting the crystal structure ofthe high-k layers. Preferably, the separating oxide film has a thicknessof no more than about 4 molecular monolayers, more preferably no morethan about 2 molecular monolayers, thereby minimizing the thickness ofthe dielectric nanolaminate while still accomplishing the interruptionof high-k crystal structure. In terms of absolute thickness, preferablythe separating oxide film has a thickness between about 3 Å and 15 Å,more preferably less than about 10 Å. This interrupting or separatinglayer is also referred to herein as an interface layer, particularly an“intermediate” interface layer. More preferably, the stack furtherincludes additional aluminum oxide or lanthanide oxide films on theouter surfaces of the high-k dielectric layers.

[0060] With reference to FIG. 4 (see also Example 6 below) a memory cellstructure 100 is shown, including 4 thin interface films alternated with3 high-k films. In particular, a dielectric nanolaminate 110 comprisesthree 30 Å high-k films 112 of ZrO₂, separated by 5 Å intermediateinterface films 113 of Al₂O₃. Additionally, the outer surfaces of theoutermost high-k films 112 are covered with 10 Å outer interface films114 of Al₂O₃. Note that the outermost aluminum oxide films are twice thethickness of the intermediate aluminum oxide films. These outerinterface layers 114 thus better serve as a barrier to oxygen and dopantdiffusion to and from conductors 116 on either side of the dielectricnanolaminate 110. It will be understood that the aluminum oxide films113, 114 can be replaced with lanthanide oxide film. Alternatively, dueto the high dielectric strength of lanthanide oxides, the zirconiumoxide films 112 can be replace by lanthanide oxides.

[0061] ALD Al₂O₃ and ALD lanthanide oxides can perfectly cover thesubstrate surface, even when the oxide layer thickness approaches thelattice constant of the metal oxide. Most of the dielectric thicknesscan be reserved for the high-k component. Thus, the capacitance densityof the layered dielectric structure made by ALD is better than thatobtained with other deposition methods. Integrated circuit (IC)capacitor applications, such as DRAM memory cell capacitors, willbenefit from the present invention.

[0062] Another benefit of the present invention is that the gate oxidethickness can be minimized without sacrificing the reliability of themanufactured devices. Either encapsulating a high-k material with anextremely thin and uniform aluminum oxide or lanthanide oxide layer,preferably by ALD, leads to excellent equivalent oxide thickness (EOT).As will be appreciated by the skilled artisan in the field of integratedcircuit design, dielectric structures layers with low EOT yet lowleakage current is beneficial in that it facilitates scaling transistorand integrated circuit designs generally. Similarly, forming a metaloxide nanolaminate by ALD produces excellent EOT with low leakagecurrent.

[0063] Atomic layer deposition (ALD) processes require volatile sourcechemicals that are thermally stable and reactive at the depositiontemperature. Sufficient volatility for purposes of ALD is defined as aminimum vapor pressure of the compound that is sufficient to cover thewhole substrate with a single molecular layer of source chemicalmolecules during the source pulse time at the deposition temperature.When using very short pulse times in the order of 0.1-0.5 s, the minimumvapor pressure of the source compound should be approximately 0.02 mbarat the deposition temperature. The deposition temperature, in turn, isselected to be above condensation temperature while below thermaldecomposition temperatures for the selected precursors, enablingadsorption without decomposition and permitting the self-limitingprocess.

[0064] As noted above, lanthanides can be made volatile with selectedligands that prevent interaction between lanthanide atoms in theprecursor or source. Examples of suitable ligands includebeta-diketonates, such as thd (thd=2,2,6,6-tetramethyl-3,5-heptanedione)and alkyldisilazanes, such as hmds (hmds=N(Si(CH₃)₃)₂). Aluminum has awide range of volatile compounds, such as halides AlCl₃, AlBr₃, AlI₃,alkoxides, such as Al(OCH₂CH₃)₃, alkyls, such as (CH₃)₃Al,beta-diketonates, such as Al(thd)₃ and anhydrous nitrate Al(NO₃)_(3.)

[0065] A skilled artisan will understand that, although the depositionexamples deal with ALD operated at about 5-10 mbar absolute reactionchamber pressure, the metal oxide nanolaminates can also be grown by ALDat a different pressure range. Other possible deposition methods at verylow pressures, e.g., molecular beam epitaxy (MBE), can be used forgrowing the metal oxide nanolaminate.

EXAMPLES Example 1 ALD of Aluminum Oxide from (CH₃)₃Al and Water

[0066] With reference again to FIG. 2, in a preferred embodiment, thealuminum source pulse 50 comprises trimethyl aluminum or TMA) ((CH₃)₃Al)fed into the reaction space. TMA chemisorbs on hydroxyl (—OH) groups onthe substrate surface. Methane is released as a byproduct. Theself-saturating surface reaction leaves a methyl-terminated aluminumoxide layer on the surface. The removal 55 comprises flowing inert gasflow to purge residual TMA and methane from the reaction space. Theoxygen source pulse 60 comprises a water pulse that reacts with themethyl groups on aluminum oxide. The self-saturating surface reactionleaves a hydroxyl-terminated aluminum oxide layer on the substratesurface and methane gas is released as a byproduct. The second removal65 also comprises flowing inert gas to purge residual water and methanefrom the reaction space. The substrate surface is now ready to receivethe next TMA pulse. Alternating TMA and H₂O reactant pulses increasesthe thickness of the aluminum oxide film uniformly over the substrateuntil a desired thickness is obtained.

[0067] A silicon wafer was loaded into the reaction space of Pulsar™2000 reactor (commercially available from ASM Microchemistry of Espoo,Finland), which is designed for ALD processes. The reaction space wasevacuated to vacuum with a mechanical vacuum pump. After evacuation thepressure of the reaction space was adjusted to about 5-10 mbar(absolute) with flowing nitrogen gas that had a purity of 99.9999%. Thenthe reaction space was stabilized at 300° C. Alternating vapor phasepulses of (CH₃)₃Al and H₂O, vaporized from external sources, wereintroduced into the reaction space and contacted with the substratesurface. The source chemical pulses were separated from each other withflowing nitrogen gas.

[0068] The pulsing cycle consisted of four basic steps:

[0069] (CH₃)₃Al pulse

[0070] N₂ purge

[0071] H₂O pulse

[0072] N₂ purge

[0073] Each of the pulsing and purging times was on the order of 0.5 s.The pulsing cycle was repeated 100 times.

[0074] After the growth process, the silicon substrate was unloaded fromthe reaction space. The growth rate of Al₂O₃ from (CH₃)₃Al and H₂O wastypically near 0.1 nm/cycle at 300° C. The number of cycles determinethe thickness of the layer, with an average of about 1 Å/cycle, or about3-4 cycles/monolayer (Al₂O₃ has a bulk lattice parameter of about 3 Å).The methyl terminations left by each TMA pulse reduce the number ofavailable chemisorption sites, such that less than a full monolayerforms with each pulse. Thus, in order to achieve the thickness rangesset forth above, preferably between 1 and 18 cycles, more preferablybetween about 3 and 12 cycles, and most preferably between about 3 and 8cycles are performed.

[0075] The Al₂O₃ layer may serve as an oxygen diffusion barrier and thusprevent the oxidation of the silicon substrate. In one embodiment, theAl₂O₃ layer serves as a seed layer for further thin film growth. Forexample, a high-k layer may be grown on the Al₂O₃ layer. In anotherembodiment silicon or silicon germanium is deposited on the Al₂O₃ layer,and the Al₂O₃ layer serves as an interfacial layer.

Example 2 ALD Processes Using Aluminum Beta-diketonates

[0076] Aluminum acetylacetonate, i.e. Al(acac)₃, andtris-(2,2,6,6-tetramethyl-3,5-heptanedionato)aluminum, i.e. Al(thd)₃,react slowly with water. In the process aluminum oxide is formed andHacac or Hthd vapor is released. Faster surface reactions are possiblewhen using ozone as an oxygen source. However, ozone is preferably usedonly for the growth of the top interfacial aluminum oxide layer, asnoted above in the discussion of preferred oxygen source materials, toavoid oxidation of the underlying substrate.

Example 3 Replacing a SiO₂ Interface Layer with Al₂O₃ by an ExchangeReaction

[0077] An ALD reactor or a CVD reactor is used for the process. Asubstrate with a silicon dioxide surface is placed into the reactionspace. The pressure can be atmospheric, but preferably the pressure ofthe reaction space is adjusted to about 1-10 mbar. The substratetemperature is adjusted to between about 300° C. and 400° C. Vaporizedaluminum compound, preferably aluminum halide and more preferablyaluminum chloride, is contacted with the substrate surface for about twominutes.

[0078] When AlCl₃ vapor is contacted with a SiO₂ surface, solid Al₂O₃ isformed on the surface and SiCl₄ vapor is formed. The Gibb's free energyof this reaction is favorable for the formation of aluminum oxide.

1.5SiO₂(s)+2AlCl₃(g)→Al₂O₃(s)+1.5SiCl₄(g) ΔG _(f)(300° C.)=−52 kJ   [2]

[0079] The completion of the exchange reaction can be monitored, e.g.with a quadrupole mass spectrometer located at the exhaust side of thereaction space. The reaction has ended when there is no volatile siliconcompound (e.g., silicon chloride) left in the gas phase of the reactionspace. The flow of the volatile aluminum compound into the reactionspace is stopped. The reaction space is preferably evacuated to removeresidual gaseous aluminum compound before unloading the substrate orcontinuing with another thin film process.

[0080] The replacement reaction depends upon diffusion of the aluminumsource chemical through the growing aluminum oxide layer, which formsfirst at the surface. Accordingly, the process is self-limiting anddesirably is conducted to form only a thin interfacial aluminum oxidelayer, with thicknesses in the ranges discussed above. For purposes ofimproved nucleation thereover, the thickness can be less than a fullmonolayer.

[0081] In one embodiment, a SiO₂ gate dielectric layer can be formedover a substrate and only a thin top portion of the SiO₂ is converted,serving as a nucleation layer for later polysilicon or poly-SiGe gateelectrode deposition, and preferably also as a diffusion barrier. Thealuminum oxide interface layer has an increased k value as compared tothe prior SiO₂ surface.

[0082] In another arrangement, a thin SiO₂ layer is completely convertedinto a thin interfacial aluminum oxide in contact with the underlyingsubstrate. The gate dielectric can be completed by deposition of ahigh-k material over the aluminum oxide interface layer, and optionallya further top interface layer of aluminum oxide.

Example 4 The Deposition of a Thin Aluminum Oxide Interface Layer

[0083] A silicon wafer was loaded into the reaction space of Pulsar™2000 reactor (ASM Microchemistry), which is designed for ALD processes.The reaction space was evacuated to vacuum with a mechanical vacuumpump. After evacuation the pressure of the reaction space was adjustedto about 5-10 mbar (absolute) with flowing nitrogen gas that had apurity of 99.9999%. Then the reaction space was stabilized at about 300°C. Alternating vapor phase pulses of (CH₃)₃Al and H₂O, vaporized fromexternal sources, were introduced into the reaction space and contactedwith the substrate surface. The source chemical pulses were separatedfrom each other at the gas phase of the reaction space with flowingnitrogen gas.

[0084] The pulsing cycle consisted of the four basic steps:

[0085] (CH₃)₃Al pulse

[0086] N₂ purge

[0087] H₂O pulse

[0088] N₂ purge

[0089] Each of the pulsing and purging times was in the order of 0.5 s.The pulsing cycle was repeated 3, 6, 9 or 12 times, representing about1, 2, 3 and 4 monolayers, respectively. After the deposition of theAl₂O₃ layer, a high-k layer was formed on the Al₂O₃ surface. The high-klayer, such as HfO₂ or ZrO₂, can be processed with ALD (see Example 5)or any other suitable deposition process, such as CVD, PVD and spin-ondeposition processes.

[0090] The lower thickness limit for the Al₂O₃ layer that separates thesilicon substrate from the high-k material is about one molecular layerto serve as a minimal thickness barrier layer against oxygen and otherdiffusion (e.g., boron diffusion). However, there were indications thateven one aluminum source chemical pulse followed by one oxygen sourcechemical pulse was sufficient to create a suitable surface for rapidnucleation and deposition of a high-k material or in situ doped siliconlayer thereover. This single-cycle process represents less than a fullmonolayer, due to the physical size of the chemisorbed species(including organic tails) from the first pulse. The upper thicknesslimit for the Al₂O₃ layer depends on the acceptable equivalent oxidethickness (EOT).

Example 5 An Aluminum Oxide Sandwich in a Gate Dielectric

[0091] A silicon wafer was dipped in HF solution to remove silicondioxide. Residual HF was washed away with purified water. Then the waferwas placed in the reaction chamber of an F450™ reactor, which iscommercially available from ASM Microchemistry Ltd. of Espoo, Finland.

[0092] Reactor conditions were set for sequential deposition of bothaluminum oxide and zirconium oxide films by ALD. The reactor wasevacuated with a mechanical pump. The pressure of the reaction chamberwas adjusted in the 5-10 mbar range with flowing nitrogen gas. Thetemperature of the reaction chamber, and thus of the substrate, was setto about 300° C. ZrCl₄ source chemical outside the reaction chamber washeated to 175° C.-180° C. Trimethyl aluminum TMA was vaporized at roomtemperature from an external source container. H₂O was used as an oxygensource. It was vaporized at room temperature from an external sourcecontainer. Any inactive gas, such as nitrogen or argon, can be used forpurging the reactor. Nitrogen was used for the experiments.

[0093] The deposition started with the growth of an Al₂O₃ layer. Analuminum oxide thin film can be prepared on a silicon substrate asdescribed above. A slightly modified process was employed in theexperiments. TMA vapor was introduced to the reaction chamber andcontacted with the wafer surface for 0.2 s. This is referred to aspulse 1. The reaction chamber was purged with nitrogen gas for 1.1 s toremove surplus TMA and byproducts from the reaction chamber. This isreferred to as purge 1. Then water vapor was introduced to the reactionchamber and exposed to the wafer surface for 1.5 s. This is referred toas pulse 2. Residual H₂O and reaction byproducts were removed by purgingthe reaction chamber for 3.0 s. This is referred to as purge 2. Duringeach of the reaction phases, the reactants are supplied in sufficientquantity for the given other parameters to saturate the surface.

[0094] This exemplary aluminum oxide deposition cycle is summarized inTable I. TABLE I Al₂O₃ Temperature Pressure Time Phase Reactant (°C.)(mbar (sec) pulse 1 TMA 300 5-10 0.2 purge 1 — 300 5-10 1.1 pulse 2 H₂O300 5-10 1.5 purge 2 — 300 5-10 3.0

[0095] This deposition cycle, consisting of pulse 1, purge 1, pulse 2and purge 2, was repeated 10 times. The deposition rate of Al₂O₃ fromTMA and H₂O is about 1 Å/cycle on average at 300° C., such that theAl₂O₃ layer thickness after 10 cycles is about 10 Å.

[0096] A high-k dielectric layer is then formed on the aluminum oxidethin film. The high-k dielectric layer may be made of any material knownin the art. Preferably the dielectric constant is greater than 5, morepreferably greater than 10.

[0097] The high-k dielectric layer can also be formed by an ALD typeprocess. The skilled artisan will appreciate, however, that the high-kdielectric material can be formed by any suitable method (e.g., MOCVD),and the advantages of the described aluminum oxide interface layers willstill obtain. In the illustrated embodiment, ZrO₂ is deposited by an ALDtype process. ZrCl₄ vapor was introduced to the reaction chamber andexposed the wafer surface for 1.5 s. This is referred to as pulse A. Thereaction chamber was purged with nitrogen gas for 3.0 s to removesurplus ZrCl₄ and byproducts from the reaction chamber. This is referredto as purge A. Then water vapor was introduced to the reaction chamberand exposed to the wafer surface for 3.0 s. This is referred to as pulseB. Residual H₂O and reaction byproducts were removed by purging thereaction chamber for 4.0 s. This is referred to as purge B. During eachof the reaction phases, the reactants are supplied in sufficientquantity for the given other parameters to saturate the surface.

[0098] This exemplary high-k deposition cycle is summarized in Table I.TABLE II ZrO₂ Temperature Pressure Time Phase Reactant (°C.) (mbar)(sec) pulse A ZrCl₄ 300 5-10 1.5 purge A — 300 5-10 3.0 pulse B H₂O 3005-10 3.0 purge B — 300 5-10 4.0

[0099] The cycle of Table I, consisting of pulse A, purge A, pulse B,purge B, was repeated 51 times. The average deposition rate is about0.59 Å/cycle at 300° C., such that the ZrO₂ thickness was about 30 Å.

[0100] In the above example, temperatures during the ZrO₂ depositionwere kept at the same temperature as the previous Al₂O₃ deposition tofacilitate rapid in situ processing. More generally, temperatures duringthe process preferably fall between about 200° C. and 500° C. For anamorphous ZrO₂ layer, the temperature is more preferably at the low endof this range, between about 200° C. and 250° C., and most preferably atabout 225° C. For a crystalline film, the temperature is more preferablyat the high end of this range, between about 250° C. and 500° C., andmost preferably about 300° C. As will be appreciated by the skilledartisan, however, mixtures of amorphous and crystalline compositionresult at the boundary of these two regimes. The illustrated processproduces a largely crystalline ZrO₂ film.

[0101] In this case, the metal monolayer formed in the metal phase isself-terminated with chloride, which does not readily react with excessZrCl₄ under the preferred conditions. The preferred oxygen source gas,however, reacts with the chloride-terminated surface during the oxygenphase in a ligand-exchange reaction limited by the supply of zirconiumchloride complexes previously adsorbed. Moreover, oxidation leaves ahydroxyl and oxygen bridge termination that does not further react withexcess oxidant in the saturative phase.

[0102] Preferably, sufficient cycles are conducted to grow between about20 Å and 60 Å of ZrO₂. More preferably, sufficient cycles are conductedto grow between about 20 Å and 40 Å. The dielectric constant of thelayer is between about 18 and 24. In the illustrated examples, 30 Å ofZrO₂ was formed.

[0103] To form an aluminum oxide sandwich, a second layer of aluminumoxide is deposited on top of the high-k layer, in this case ZrO₂, alsoby the ALD Al₂O₃ process described above and summarized in Table I.Desirably, the structure was coated with another 10 Å of aluminum oxide.Thus, the dielectric sandwich comprised 10 Å Al₂O₃/30 Å ZrO₂/10 Å Al₂O₃.The second layer of aluminum oxide serves as a nucleation layer forsubsequent deposition of a polysilicon or poly-SiGe gate electrodelayer, and more preferably also serves as a minimum thickness to serveas a diffusion barrier between the high-k material and a secondmaterial.

[0104] The remaining components of a gate stack are formed on the upperlayer of aluminum oxide by methods well known in the art.Advantageously, known CVD processes for depositing doped silicon andpoly-SiGe layers nucleate rapidly on Al₂O₃, improving overallthroughput. The aluminum oxide layers present between the substrate andthe high-k material and between the high-k material and the gateelectrode act as diffusion barriers and allow the gate dielectric tofunction properly. In addition, the aluminum oxide layers help tostabilize the high-k material, allowing for a repeatable, productionworthy process of manufacturing gate electrodes in integrated circuits.

[0105] Another experiment was made where the thicknesses of thedeposited thin films were as follows: 5 Å Al₂O₃/30 Å ZrO₂/5 Å Al₂O_(3.)

Example 6 ZrO₂/Al₂O₃ Nanolaminate

[0106] Still another experiment was made where the thin film consistedof a metal oxide nanolaminate. Several layers of ZrO₂ and amorphousAl₂O₃ were grown. The processes of Tables I and II above were employed,forming a structure similar to that of FIG. 4. The structure was asfollows:

10 Å Al₂O₃/5 Å ZrO₂/5 Å Al₂O₃/5 Å ZrO₂/5 Å Al₂O₃/5 Å ZrO₂/10 Å Al₂O_(3.)

[0107] Current leakage through the structures was very small andremarkably small EOTs (equivalent oxide thicknesses) were obtained.

GENERAL DISCUSSION

[0108] The selection of source chemical combinations depends on thelocation of the interface. When depositing an interface layer on siliconby ALD, highly oxidative source chemicals should be avoided. It ispreferable to use a relatively mild oxygen source such as water. Waterreacts quickly with alkyl aluminum compounds but does not oxidizesilicon, especially when the substrate temperature is below 300° C.

[0109] When depositing an Al₂O₃ interface layer on high-k material byALD, mild oxygen sources as well as highly oxidative source chemicals(e.g., ozone) can be used.

[0110] Those skilled in the art will understand that the deposition ofthe Al₂O₃ interface layer is not limited to the ALD method. Example 3,for example, provides a different but also self-limiting process forthin aluminum oxide layer formation. Furthermore, other CVD, MOCVD orPVD methods can be applied as long as a sufficiently uniform filmcovering the substrate is obtained.

[0111] It will be appreciated by those skilled in the art that variousomissions, additions and modifications may be made to the processesdescribed above without departing from the scope of the invention, andall such modifications and changes are intended to fall within the scopeof the invention, as defined by the appended claims.

We claim:
 1. An integrated circuit comprising an interface layer betweena conductive material and a dielectric material, the interface layerselected from the group consisting of aluminum oxide and lanthanideoxides and having a thickness less than or equal to about 4 molecularmonolayers.
 2. The integrated circuit of claim 1, wherein the conductivematerial comprises silicon.
 3. The integrated circuit of claim 1,wherein the conductive material is a single-crystal silicon structure.4. The integrated circuit of claim 1, wherein the conductive material isa silicon-germanium alloy.
 5. The integrated circuit of claim 1, whereinthe dielectric material is characterized by a dielectric constantgreater than about
 10. 6. The integrated circuit of claim 5, furthercomprising a second interface layer directly contacting an opposite sideof the dielectric material, and a second conductive material directlyover the second interface layer, the second interface layer selectedfrom the group consisting of aluminum oxide and lanthanide oxides andhaving a thickness of less than or equal to about 4 molecularmonolayers.
 7. The integrated circuit of claim 6, wherein the conductivematerial comprises a silicon substrate, wherein the second conductivematerial comprises a gate electrode, and wherein the interface layer,dielectric material and second interface layer form a gate dielectricfor an integrated transistor.
 8. The integrated circuit of claim 6,wherein the conductive material comprises a storage electrode in amemory cell, and the second conductive material comprises a referenceelectrode, wherein the interface layer, dielectric material and secondinterface layer form a capacitor dielectric for an integrated capacitor.9. The integrated circuit of claim 5, wherein the interface layer has athickness between about 3 Å and 15 Å.
 10. The integrated circuit ofclaim 9, wherein the interface layer has a thickness between about 3 Åand 9 Å.
 11. The integrated circuit of claim 1, further comprising aplurality of alternating interface and dielectric layers, each interfacelayer selected from the group consisting of aluminum oxide andlanthanide oxides and having a thickness between about 1 Å and 15 Å,each dielectric layer having a dielectric constant of greater than about5.
 12. The integrated circuit of claim 11, wherein each interface layercomprises aluminum oxide and each dielectric layer comprises zirconiumoxide.
 13. A high-k dielectric structure in an integrated circuitcomprising a first aluminum oxide layer, a high-k material layerdirectly over the first aluminum oxide layer, and a second layer ofaluminum oxide directly over the high-k material layer, wherein thehigh-k material layer is characterized by a dielectric constant greaterthan about
 5. 14. The high-k dielectric structure of claim 13, whereinthe high-k material is selected from the group consisting of zirconiumoxide (ZrO₂), titanium oxide (TiO₂), tantalum oxide (Ta₂O₅), bariumstrontium titanate (BST), strontium titanate (ST), barium titanate (BT),lead zirconium titanate (PZT), and strontium bismuth tantalate (SBT).15. The high-k dielectric structure of claim 13, wherein each of thefirst aluminum oxide layer and the second aluminum oxide layer have athickness of less than or equal to about two monolayers.
 16. A capacitorstructure in an integrated circuit, comprising: a first conductor; afirst oxide layer directly overlying the first conductor, the firstoxide layer comprising a material selected from the group consisting ofaluminum oxide and lanthanide oxides; a dielectric material directlyoverlying the first oxide layer; a second oxide layer directly overlyingthe dielectric material, the second oxide layer comprising a materialselected from the group consisting of aluminum oxide and lanthanideoxides; and a second conductor overlying the second oxide layer.
 17. Thecapacitor structure of claim 16, wherein the oxide layers are depositedby ALD.
 18. The capacitor structure of claim 16, wherein the firstconductor comprises a single-crystal silicon substrate.
 19. Thecapacitor structure of claim 16, wherein the dielectric material has adielectric constant of at least about
 5. 20. The capacitor structure ofclaim 19, wherein the dielectric material is selected from the groupconsisting of zirconium oxide (ZrO₂), hafnium oxide (HfO₂), titaniumoxide (TiO₂), tantalum oxide (Ta₂O₅), barium strontium titanate (BST),strontium titanate (ST), barium titanate (BT), lead zirconium titanate(PZT), lead strontium titanate (PST), strontium bismuth tantalate (SBT),tantalum oxynitride (Ta_(x)O_(y)N_(z)) and niobium oxynitride(Nb_(x)O_(y)N_(z)).
 21. The capacitor structure of claim 16, wherein thesecond conductor is a transistor gate electrode comprising SiGe.
 22. Thecapacitor structure of claim 16, wherein the second conductor directlycontacts the second oxide layer.
 23. An oxide layer located between twomaterials, wherein the oxide layer prevents diffusion of molecules fromone material to the other, the oxide layer selected from the groupconsisting of aluminum oxide and lanthanide oxides, the oxide layerhaving a thickness between one full molecular monolayer and about 4molecular monolayers.
 24. A method of preventing the oxidation of asubstrate during high-k material deposition, comprising: forming a layerof aluminum oxide on the substrate; and depositing the high-k material,having a dielectric constant greater than about 5, directly over thealuminum oxide layer.
 25. The method of claim 24, wherein the layer ofaluminum oxide has a thickness between about 3 Å and 15 Å.
 26. Themethod of claim 24, wherein forming the layer of aluminum oxidecomprises depositing the layer of aluminum oxide on the substrate by anALD type process.
 27. The method of claim 26, further comprisingexposing the substrate to an ALD preparation pulse prior to depositingthe layer of aluminum oxide by the ALD type process.
 28. The method ofclaim 27, wherein the ALD preparation pulse comprises providing a mildoxidant over a hydrogen terminated surface of the substrate.
 29. Themethod of claim 28, wherein the mild oxidant comprises water.
 30. Themethod of claim 24, wherein forming the layer of aluminum oxide on thesubstrate comprises exposing a silicon oxide layer on the substrate toan aluminum halide.
 31. The method of claim 30, wherein the aluminumhalide comprises AlCl_(3.)
 32. The method of claim 30, wherein exposingthe silicon oxide layer on the substrate to an aluminum halidecompletely converts the silicon oxide layer to aluminum oxide by anexchange reaction.
 33. A process for forming a dielectric stack in anintegrated circuit, the process comprising at least one of the followingcycle: forming no more than about one monolayer of an aluminum orlanthanide complex over a semiconductor substrate by exposure to a firstreactant species; reacting an oxygen source gas with the first materialto leave no more than about one monolayer of aluminum oxide orlanthanide oxide over the semiconductor substrate.
 34. The process ofclaim 33, further comprising repeating the cycle between about 3 and 15times to form an aluminum oxide or lanthanide oxide interface layer. 35.The process of claim 34, further comprising depositing a dielectricmaterial with a dielectric constant of at least about 5 directly overthe interface layer.
 36. The process of claim 35, further comprisingrepeating the cycle at least once after depositing the dielectricmaterial to form a top aluminum oxide or lanthanide oxide interfacelayer.
 37. The process of claim 36, further comprising depositing asilicon-containing layer over the second interface layer.
 38. Adielectric nanolaminate structure, comprising at least three alternatinglayers of crystalline and amorphous metal oxides, including amorphousmetal oxide layers on outside surfaces of the nanolaminate structure.39. The dielectric nanolaminate structure of claim 38, wherein thecrystalline metal oxide comprises a material having a dielectricconstant greater than about
 10. 40. The dielectric nanolaminatestructure of claim 38, wherein the crystalline metal oxide comprises anoxide of a metal in one of groups 4 and 5 of the periodic table ofelements.
 41. The dielectric nanolaminate structure of claim 38, whereineach amorphous metal oxide has a thickness between about 3 Å and 15 Å.42. A nanolaminate structure, comprising at least two high-k layersseparated by an intermediate oxide layer selected from the groupconsisting of aluminum oxide and lanthanide oxides, the high-k layerseach characterized by a dielectric constant greater than about 10, theintermediate oxide layer having a thickness of no more than about 10 Å.43. The nanolaminate structure of claim 42, further comprising outeroxide layers on an outer side of each of the two high-k layers, theouter oxide layers selected from the group consisting of aluminum oxideand lanthanide oxides and having thicknesses of no more than about 4molecular monolayers.
 44. The nanolaminate structure of claim 43,wherein the outer oxide layers have thicknesses between about 1molecular monlayer and 2 molecular monlayers.
 45. The nanolaminatestructure of claim 43, wherein the outer oxide layers have a thicknessof about 10 Å and the intermediate oxide layer has a thickness of about5 Å..